1. Field of the Invention
The present invention relates to a packaging container for airtightly enclosing food, feed and the like and storing such food or the like without causing any deterioration of quality to the food or the like. The present invention also relates to a packaged food or the like in which food or the like is enclosed in the aforementioned packaging container and can be stored for a long period without experiencing any deterioration of quality thereof.
2. Prior Art
Techniques for enclosing food in an airtight container such as a can, a bottle or the like in order to store the food for a long period has been conventionally known. Among such preserved food, packaged food in which food is airtightly enclosed in a plastic container or the like has been increasingly utilized for various cases, because of the relatively light weight and low packaging cost thereof. In such packaged food, in general, as an attempt to prevent deterioration of quality during storage, food is enclosed under vacuum or nitrogen substitution or a deoxidizer is enclosed together with the food so that oxidization is slowed, or alternatively, the packaged food is stored in a freezer so that the rate of deterioration is slowed.
However, in the case of coffee beans which have just been roasted, for example, the beans release carbon dioxide gas as time elapses. The beans cannot be stored in an unsealed container, however, because then the aromatic components thereof will be dispersed outside and the flavor will be marred. Therefore, conventionally, such freshly-roasted coffee beans cannot but be stored in an airtight pressure resistant container and any other adequate preservation means has not been available. In addition, in the case of pickles like Korean pickles, sterilization at a high temperature cannot be carried out because such a high temperature may deteriorate the flavor of the pickles. Conventional airtight containers for packaging food having a simple structure is not likely to work, either, because there is a possibility that the sealed container with pickles enclosed therein explodes due to the increase in the pressure inside the container (such increase in the internal pressure is caused by the fermentation during storage). Accordingly, in order to preserve food or feed which may increase the pressure inside the container during storage, such as coffee beans, fermented food or silage feed, in a manner in which the flavor or the quality thereof is not damaged, it is necessary to employ a container equipped with a safe valve which valve operates only when the pressure inside the container exceeds the pressure outside the container by a predetermined value.
However, the conventional safe valve which can be used for the aforementioned purpose is essentially a precision device, which is quite expensive, and is not suitable for use in a container for storing a relatively small portion of processed food or feed and the like. On the other hand, conventional techniques for preventing explosion of a container when packaged food is heated by a microwave oven have been proposed (e.g., Japanese Utility Model 62-69466, Japanese Utility Model 63-156978). In these conventional techniques, a vent hole formed at a portion of the packaging container is sealed by a sealing piece attached to the vent hole, in a manner in which the sealing piece is peeled off due to the pressure of steam generated by heating, thereby preventing the packaging container from exploding. However, in these techniques, leakage of the content of the package and/or entry of air outside the package into the package cannot be suppressed once the vent hole is opened, and storage cannot be adequately continued thereafter. Therefore, these techniques cannot be a solution of the aforementioned problems.
A first object of the present invention is to provide an economical packaging container which, when fermented food or the like and silage feed as described above are enclosed therein for storage, is reliably prevented from exploding, although the pressure inside the container is increased, thereby eliminating the possibility of the content of the container bursting outside of the container or the quality of the content being deteriorated.
In addition, a second object of the present invention is to provide an economical packaged food and packaged feed, in which the food or feed can be preserved for a long period without experiencing deterioration of quality, although the conditions in the environment are significantly changed.
The packaging container of the present invention, which can achieve the aforementioned objects, is a gas-impermeable container sealed by an adhesive hole-sealing sheet, characterized in that the hole-sealing sheet is formed by providing, on a back surface of a gas-impermeable sheet base material whose bending strength (S) represented by the following formula (A) is no less than 0.20 m3/N, a pressure sensitive adhesive layer whose vertical peeling strength at 40xc2x0 C., with respect to a surface of the container in which at least a vent hole is formed, is in the range of 0.3-2 N/cm.
In addition, the container of the present invention is preferably formed by plastic or metallized plastic. Further, the container of the present invention preferably has a bag-like shape.
S=L/W(m3/N)xe2x80x83xe2x80x83(A)
wherein
L: Critical length measured by a Clark degree testing machine (m)
W: Weight per 1 m2 of the sheet base material (N/m2)
Further, the packaged food or the packaged feed of the present invention, which can achieve the aforementioned second object, is characterized in that desired food or feed is enclosed in the container having the structure as described above.